1. Field of the Invention
The present invention relates to an organic electroluminescent display (ELD) device, and more particularly, to an organic electroluminescent display device where aperture ratio and resolution are improved due to an arrangement of organic patterns in sub-pixel regions and a method of fabricating the organic ELD device.
2. Discussion of the Related Art
Although a cathode ray tube (CRT) was widely used as a display device, a flat panel display (FPD) such as a plasma display panel (PDP) device, a liquid crystal display (LCD) device and an organic electroluminescent display (ELD) device, which may be referred to as an organic light emitting diode (OLED) device, has been the subject of recent research and development.
Among various FPD devices, the organic ELD device of an emissive type has advantages of a light weight and a thin profile due to omission of a backlight unit. In addition, the organic ELD device has a viewing angle and a contrast ratio superior to the LCD device, and has advantages in a power consumption such that the organic ELD device is driven with a low direct current (DC) voltage. Further, the organic ELD device has a fast response speed, an excellent durability against an external impact and a wide operation temperature range. Specifically, since the fabrication process for the organic ELD device is simple, the organic ELD device has a lower production cost as compared with the LCD device. Recently, a flexible organic ELD device using a flexible substrate such as a plastic has been suggested as a FPD device for next generation. The flexible organic ELD device displays images even when the flexible ELD device is bent like a paper.
The organic ELD device emits a light using an organic electroluminescent diode. FIG. 1 is band diagram of an organic electroluminescent for an organic electroluminescent display device according to the related art. In FIG. 1, an organic electroluminescent diode 10 includes an anode 21, a hole injection layer (HIL) 37, a hole transporting layer (HTL) 33, an emission material layer (EML) 40, an electron transporting layer (ETL) 35, an electron injection layer (EIL) 39 and a cathode 25. The HIL 37 is disposed between the anode 21 and the HTL 33 and the EIL 39 is disposed between the cathode 25 and the ETL 35 for improving an emission efficiency. In addition, the EML 40 is disposed between the HTL 33 and the ETL 35.
When positive and negative voltages are applied to the anode 21 and the cathode 25, respectively, holes of the anode 21 and electrons of the cathode 25 are transported to the EML 40 to form excitons. In addition, when an excited state of the excitons is transited to a ground state, a light generated in the EML 40 is emitted as a visible light.
An organic emission layer including the HIL 37, the HTL 33, the EML 40, the ETL 35 and the EIL 39 may be fabricated through a vacuum thermal evaporation method. In the vacuum thermal evaporation method, an organic material for the organic emission layers is disposed on a evaporation source, for example, a filament, a basket and a boat, in a vacuum chamber, and a substrate is disposed over the evaporation source. After the organic material on the evaporation source is heated up, a shutter between the evaporation source and the substrate is open and the evaporated organic material is deposited on the substrate. A shadow mask having a plurality of open portions is used for a plurality of organic patterns of the organic material. After the shadow mask may be disposed adjacent to the substrate, the organic material is deposited to the substrate through the plurality of open portions of the shadow mask to form the plurality of organic patterns of the organic material.
FIG. 2 is a plan view showing a single pixel region of an organic electroluminescent display device according to the related art. In FIG. 2, an organic electroluminescent display (ELD) device includes a pixel region P and the pixel region P includes first, second and third sub-pixel regions SP1, SP2 and SP3. First, second and third organic patterns 60 are formed in the first, second and third sub-pixel regions SP1, SP2 and SP3, respectively. For example, the first, second and third organic patterns 60 may emit red, green and blue (R, G and B) colored lights, respectively. When each of the first, second and third organic patterns 60 has substantially the same area and the same size as each of the first, second and third sub-pixel regions SP1, SP2 and SP3, a border portion between the adjacent two sub-pixel regions does not emit a predetermined colored light due to overlapping, which may be referred to as a shadowing effect. To prevent the shadowing effect, the adjacent organic patterns 60 may be spaced apart by a first distance d1. For example, each of the first, second and third organic patterns 60 may have an area of about 18% of each of the first, second and third sub-pixel regions SP1, SP2 and SP3. Accordingly, the organic ELD device may have an aperture ratio of about 18%.
The portion between the adjacent organic patterns 60 may be referred to as a dead zone that is not used for emission of light. As a resolution of the organic ELD device increases, the number of pixel regions in a unit area increases. However, since the first distance d1 is not reduced in a vacuum thermal evaporation method, the size of the dead zone is not reduced without the shadowing effect and the size of the organic patterns 60 is reduced for a higher resolution. As a result, the aperture ratio and the lifetime of the organic ELD device are further reduced.